A wide variety of machines have been developed and disclosed which may be utilized to ream or drill out the residue deposited in heat exchanger and similar tubing. In many of those machines, a cutterhead may be threadedly mounted on the end of a drive shaft. Thus, as the drive shaft is rotated about its axis and moved longitudinal along its axis, the cutterhead may be driven through a tube to ream out any undersirable deposits and/or to enlarge the inner diameter of the tube.
An example of such a machine has been illustrated in my U.S. Pat. No. 4,015,304, issued Apr. 5, 1977. As taught in that patent, hydraulic flushing during the reaming operation may be accomplished by discharging fluid under pressure through the cutterhead in the area of the cutting. Consequently, the fluid will cool the cutterhead as well as flush away the waste material.
In order to accomplish this, the drive shaft has been provided with a hollow passage extending along the axis thereof. At one end of the drive shaft, a female threaded section may be formed in the wall of the passage. The cutterhead may be provided with a threaded end or stud which can be turned into the thread in the passage of the drive shaft in order to operatively connect the cutterhead to the drive shaft. The cutterhead may be provided with one or more passages which extend through the stud and communicate with the passage of the drive shaft. The cutterhead passages may extend to the surface of the cutterhead in the vicinity of the cutting edges. Thus, as fluid is moved under pressure through the drive shaft, it will be forced through the cutterhead openings in the vicinity of the cutting operation.
In the prior art devices, as the drive shaft is moved in rotational and longitudinal motion, significant torque and torsional forces are exerted on the cutterhead and, therefore, are transmitted into the drive shaft. For example, near the end of the threaded stud of the cutterhead, a shoulder may be formed for abutment with the end face of the drive shaft. As the cutting operation takes place, reaction forces generated by the cutting are transmitted through the cutterhead back to the drive shaft. Since the drive shaft has already been weakened at the threaded portion thereof, i.e., it has a thinner wall at the threaded portion than further along the axis, those reaction forces will tend to deform the drive shaft. For example, such deformation may cause a "flanging" of the end of the drive shaft such that the latter tends to expand around the end.
Flanging and weakening of the drive shaft may also cause a split to occur in the wall of the shaft extending from the end and generally parallel to the shaft axis. In other words, reaction of the cutterhead against the work piece will tend to cause the cutterhead to move to a position in which its axis intersects the axis of the drive shaft obliquely, rather than be located so as to be co-axial therewith. This movement causes a deformation in the drive shaft, resulting not only in destruction of the shaft, but also in damage to the work piece.
Accordingly, it has become necessary to devise structure which may be simply and inexpensive employed to prevent such damage without requiring a total redesign of available machinery.